1. Field of the Invention
This invention relates to a printing machine, such as a flexographic printing machine, of the type comprising a plurality of inking units, a plurality of plate cylinders and at least one impression cylinder which, during a printing operation, is driven by a central gear in mesh with plate cylinder gears. The plate cylinders are mounted on plate cylinder carriages, on tracks included in the machine frame, and which extend in approximately tangential to radial directions relative to the central gear. The plate cylinders are movable into engagement with the impression cylinder for the printing operation and are movable away from the impression cylinder. The inking units comprise halftone rollers, which carry halftone roller gears in mesh with the plate cylinder gears, and the halftone rollers are movable by inking unit carriages on tracks of the plate cylinder carriages. The machine also has means for aligning the teeth of the central gear with the teeth of the plate cylinder gears when the latter have been moved to pushed-in positions, datum marks provided on the plate cylinder gears and feelers, secured to the carriages for cooperating with the datum marks, for ensuring that the plate cylinders are properly aligned or adapted to be aligned for printing in register.
2. Description of the Prior Art
In a flexographic printing machine, the plate cylinders generally must be changed after each print job and the printing format may also have to be changed. The number of plate cylinders to be changed will depend on the number of colors to be printed. For each print job the plates of the plate cylinders must be properly adjusted relative to each other so that a web moving through the machine will be printed in register. To ensure printing in register, it is necessary to establish accurate meshing between the plate cylinder gears and the central gear. It is also desirable that printing be resumed after as short as possible a change-over time and that prolonged downtimes of expensive printing machines be avoided to the extent possible.
In a printing machine of the kind hereinbefore described and disclosed, for example, in published German Pat. Application No. 34 37 216, the need for expensive adjusting work after a changeover of the printing machine is substantially eliminated. A certain amount of adjusting work however, must still be performed by hand in the known machine, because the gears for driving the plate cylinders must be rotated by hand until the feeler, consisting of a lever, snaps into the associated datum mark, which is constituted by a setting bore.